1. Technical Field
The invention relates to a light source device, a lighting device, a monitoring device, and an image display apparatus, and particularly to a technology of a light source device having a plurality of light emission units.
2. Related Art
Recently, a technology of a light source device which uses laser beam source as a light source for an image display apparatus such as a projector has been proposed. The laser beam source has been developed as the light source of the image display apparatus with output increase and color multiplication of the image display apparatus. When compared with UHP lamp used as a light source of an image display apparatus in related art, the laser beam source has advantages such as high color reproducibility, instant lighting, and long life. Currently, there is a demand for luminance increase of the image display apparatus. For increasing output of the laser beam source, a semiconductor element having a plurality of light emission units for emitting light is used, for example. Since a large proportion of current supplied to the semiconductor element is converted into heat, higher heat release efficiency is required for the laser beams source as the density of the light emission units increases. When heat release is insufficient, the temperature of the semiconductor element rises. As a result, light emission efficiency of the semiconductor element lowers. Moreover, deterioration of the semiconductor element increases with the rise of the temperature of the semiconductor element, and thus the life of the laser beam source becomes short. For overcoming these drawbacks, JP-A-2002-141604 proposes a method which separates the plural light emission units into a main light emission group and a sub light emission group provided in different areas, and switches operation between the main light emission group and the sub light emission group, for example. When the light amount of the entire main light emission group lowers during drive of the main light emission group, the main light emission group is switched to the sub light emission group. By this method, the entire output of the laser beam source is maintained, and also the life of the overall laser beam source is extended.
Both of the light emission units constituting the main light emission group and the sub light emission group are arranged with a pitch capable of reducing effect on the light emission efficiency and life of the semiconductor element. In this case, the area of the semiconductor element increases by the separation of the main light emission group and sub light emission group in different regions. The manufacturing cost of the semiconductor element greatly depends on the number of semiconductor elements which can be produced from one piece of wafer. Thus, the cost of the laser beam source rises as the size of the semiconductor element increases. Moreover, the position of the light emission area considerably changes from the period of driving the main light emission group to the period of driving the sub light emission group. Thus, there is a possibility that utilization efficiency of light emitted from the laser beam source lowers in devices and optical systems using this type of laser beam. According to the related art, therefore, the size of the element for emitting light increases and the position of the light emission area considerably changes when higher light emission efficiency and longer life of the light source device are desired.